Synthesis of pharmacologically active hydrogels based on combined silicon and titanium polyolates

The target synthesis of new biologically active hydrogels based on combined silicon and titanium polyolates was carried out. The optimum conditions for hydrogel formation and their composition were determined. The type of hydrogels and mechanisms of gelation depend on the nature of polyols: gels based on combined silicon and titanium polyethylene glycolates are polymeric and formed via the polycondensation mechanism, whereas gels based on combined silicon and titanium glycerolates are colloidal and formed via the coagulation-condensation mechanism. The combined hydrogels based on silicon dimethyl glycerolates and titanium tetraglycerolate exhibit enhanced transcutaneous, wound healing, and regenerating activity.     

Catalytic transformation of silicon tetraisocyanate Si(NCO)4 to a polymeric silylcarbodiimide

A new way for the preparation of inorganic polymeric carbodiimide‐based networks is presented which resembles the transformation of molecular isocyanates using 1‐phenyl‐3‐methyl‐2‐phospholene‐1‐oxide as a catalyst. The respective reaction sequence, well established in preparative organic chemistry, has been applied for the synthesis of carbodiimide‐based SiNC(O) materials. Starting from Si(NCO)₄ (silicon tetraisocyanate), a transformation to an insoluble extended inorganic array was achieved in boiling dodecan (T = 216 °C). Analysis of the polymer using X‐ray diffraction, FT‐IR, density measurement, matrix‐assisted laser desorption/ionization time of flight and TGA revealed that this highly moisture‐sensitive amorphous network consists of oligomers of high molar mass and exhibits a high density of around 1.5 g cm^?3, which corresponds quite well to the calculated density of crystalline Si(NCN)₂ reported in the literature. Degradation of this 'SiNC(O) phase' with the release of N₂ and (CN)₂ finally provided SiC as the only crystalline product. No indication of the formation of crystalline Si₃N₄ or intermediate crystalline 'SiC₂N₄', silicon carbodiimide (= Si(NCN)₂), was noticed. Copyright © 2013 John Wiley & Sons, Ltd.     

catena‐Poly­[[di­aqua­lithium(I)]‐μ‐[9H‐purine‐2,6(1H,3H)‐dionato‐O2:N7]]

In the title compound, [Li(C₅H₃N₄O₂)(H₂O)₂]_n, the coordinate geometry about the Li⁺ ion is distorted tetrahedral and the Li⁺ ion is bonded to N and O atoms of adjacent ligand mol­ecules forming an infinite polymeric chain with Li—O and Li—N bond lengths of 1.901 (5) and 2.043 (6) Å, respectively. Tetrahedral coordination at the Li⁺ ion is completed by two cis water mol­ecules [Li—O 1.985 (6) and 1.946 (6) Å]. The crystal structure is stabilized both by the polymeric structure and by a hydrogen‐bond network involving N—H?O, O—H?O and O—H?N hydrogen bonds.     

2‐Ethyl‐6‐methylpyridin‐3‐ol and its salt bis(2‐ethyl‐3‐hydroxy‐6‐methylpyridinium) succinate

The title compounds, C₈H₁₁NO, (I), and 2C₈H₁₂NO⁺·C₄H₄O₄²⁻, (II), both crystallize in the monoclinic space group P2₁/c. In the crystal structure of (I), intermolecular O—H...N hydrogen bonds combine the molecules into polymeric chains extending along the c axis. The chains are linked by C—H...π interactions between the methylene H atoms and the pyridine rings into polymeric layers parallel to the ac plane. In the crystal structure of (II), the succinate anion lies on an inversion centre. Its carboxylate groups interact with the 2‐ethyl‐3‐hydroxy‐6‐methylpyridinium cations via intermolecular N—H...O hydrogen bonds with the pyridine ring H atoms and O—H...O hydrogen bonds with the hydroxy H atoms to form polymeric chains, which extend along the [01] direction and comprise R₄⁴(18) hydrogen‐bonded ring motifs. These chains are linked to form a three‐dimensional network through nonclassical C—H...O hydrogen bonds between the pyridine ring H atoms and the hydroxy‐group O atoms of neighbouring cations. π–π interactions between the pyridine rings and C—H...π interactions between the methylene H atoms of the succinate anion and the pyridine rings are also present in this network.     

Poly[[μ‐(1‐azaniumylethane‐1,1‐diyl)bis(hydrogen phosphonato)]sodium]: a powder X‐ray diffraction study

The title two‐dimensional coordination polymer, [Na(C₂H₈NO₆P₂)]_n, was characterized using powder X‐ray diffraction data and its structure refined using the Rietveld method. The asymmetric unit contains one Na⁺ cation and one (1‐azaniumylethane‐1,1‐diyl)bis(hydrogen phosphonate) anion. The central Na⁺ cation exhibits distorted octahedral coordination geometry involving two deprotonated O atoms, two hydroxy O atoms and two double‐bonded O atoms of the bisphosphonate anion. Pairs of sodium‐centred octahedra share edges and the pairs are in turn connected to each other by the biphosphonate anion to form a two‐dimensional network parallel to the (001) plane. The polymeric layers are connected by strong O—H...O hydrogen bonding between the hydroxy group and one of the free O atoms of the bisphosphonate anion to generate a three‐dimensional network. Further stabilization of the crystal structure is achived by N—H...O and O—H...O hydrogen bonding.<!?tpb=18.7pt>     

trans‐Diaquabis(3‐hydroxybenzoato‐κO1)bis(nicotinamide‐κN1)copper(II)

The title compound, [Cu(C₇H₅O₃)₂(C₆H₆N₂O)₂(H₂O)₂], is a two‐dimensional hydrogen‐bonded supramolecular complex. The Cu^II ion resides on a centre of symmetry and is in an octahedral coordination environment comprising two pyridine N atoms, two carboxylate O atoms and two O atoms from water molecules. Intermolecular N—H...O and O—H...O hydrogen bonds produce R₂²(4), R₂²(8) and R₂²(15) rings which lead to one‐dimensional polymeric chains. An extensive two‐dimensional network of N—H...O and O—H...O hydrogen bonds and C—H...π interactions are responsible for crystal stabilization.     

The polyoctahedral silsesquioxane (POSS) 1,3,5,7,9,11,13,15‐octaphenylpentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane (octaphenyl‐POSS)

Solvent‐free single crystals of 1,3,5,7,9,11,13,15‐octaphenylpentacyclo[9.5.1.1^3,9.1^5,15.1^7,13]octasiloxane (abbreviated as octaphenyl‐POSS), C₄₈H₄₀O₁₂Si₈, were obtained by dehydration/condensation of the tetrol Si₄O₄(Ph)₄(OH)₄. The powder pattern generated from the single‐crystal data matches well with the experimentally measured powder pattern of commercial octaphenyl‐POSS. The geometry of the centrosymmetric molecule in the crystal was compared with that in the gas phase, and had shorter Si—O bond lengths and a broader range of Si—O—Si bond angles. The average Si—O bond length [1.621 (3) Å], and Si—O—Si and O—Si—O bond angles [149 (5) and 109 (1)°, respectively] were within the same range measured previously for octaphenyl‐POSS solvates.     

Poly[[diaqua­cadmium(II)]‐μ4‐[N‐(phosphonato­methyl)ammonio]acetato]

The title compound, [Cd(C₃H₆NO₅P)(H₂O)₂]_n, is a three‐dimensional polymeric complex. The asymmetric unit contains one Cd atom, one N‐(phosphono­methyl)glycine zwitterion [(O⁻)₂OPCH₂NH₂⁺CH₂COO⁻] and two water mol­ecules. The coordination geometry is a distorted CdO₆ octa­hedron. Each N‐(phosphono­methyl)glycine ligand bridges four adjacent water‐coordinated Cd cations through three phospho­nate O atoms and one carboxyl­ate O atom, like a regular PO₄³⁻ group in zeolite‐type frameworks. One‐dimensional zigzag (–O—P—C—N—C—C—O—Cd–)_n chains along the [101] direction are linked to one another via Cd—O—P bridges and form a three‐dimensional network motif with three types of channel systems. The variety of O—H⋯O and N—H⋯O hydrogen bonds is likely to be responsible for stabilizing the three‐dimensional network structure and preventing guest mol­ecules from entering into the channels.     

Nonhydrolytic synthesis and structural study of methoxyl-terminated polysiloxane D/Q resins

Low-viscosity, methoxylated polysiloxane resins incorporating Me₂SiO_2/2 (D) and SiO_4/2 (Q) units were prepared using nonhydrolytic condensation between Si—Cl and Si—OMe groups with the formation of MeCl, catalyzed by a Lewis acid. With the commonly used catalysts, condensation between two Si—OMe groups, with formation of Me₂O, also took place to a large extent, hindering the control of the degree of condensation of the resins. Several catalysts were tested by monitoring the formation of MeCl and Me₂O using sealed NMR tubes and ¹H-NMR spectroscopy. The best compromise between reactivity and selectivity was obtained with ZrCl₄. Resins with various compositions were prepared in the absence of solvent by condensation between Me₂SiCl₂ and Si(OMe)₄ at 130°C, catalyzed by 1 mol % ZrCl₄. They were characterized using viscosimetry, gas chromatography coupled with mass-spectrometry (GC-MS), and quantitative ²⁹Si-NMR spectroscopy. The resins consisted of a complicated mixture of oligomers, linear or branched (n > 1) and cyclic (n > 3), with a high degree of D/Q bonding. The distribution of Si—OMe and Si—OSi bonds and the bonding between D and Q units were found to be nearly random. This was ascribed to the occurrence of Si—OSi/Si—OMe and Si—OSi/Si—OSi redistribution reactions that reached equilibrium during the synthesis. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2415–2425, 1998     

Incorporation of niobium into bridged silsesquioxane based silica networks

In this work different synthesis routes were evaluated with the aim of optimizing the incorporation of niobium within a hybrid silica matrix on an atomic scale. The fast kinetics of the hydrolysis/polycondensation of the organic Nb precursor Nb(OEt)₅ entails a segregation of the resulting material into Nb₂O₅ and a silica based network. To overcome this effect we (a) performed a prehydrolysis of 1,2-bis-triethoxy-ethane (BTESE) prior to adding niobium penta-ethoxide, or (b) attempted to reduce the availability of Nb via a complexation of Nb by either acetylacetone or 2-methoxyethanol. The network organization was evaluated from results of Fourier transform infrared as well as ¹³C, ²⁹Si and ¹⁷O MAS NMR spectroscopy. Whereas the prehydrolysis of BTESE and the addition of 2-methoxyethanol induced only moderate mixing of Nb and Si, leading to a network in which islands of Nb₂O₅ are linked to the hosting silica based matrix via Nb–O–Si bonds, the use of acetylacetonate lead to a mixing of Nb and Si on the atomic scale, forming a mixed Nb–O–Si network without any extended clusters of segregated Nb₂O₅. The Si–C–C–Si bridge from the silsesquioxane is found to survive the condensation process and is even present in the resulting materials after annealing at 200 °C.     

Two modifications of a five‐coordinate silicon complex

TBPY‐5‐34‐(Butane‐1,4‐diyl)(2‐{[1‐(2‐oxidophenyl)ethylidene‐κO]amino‐κN}ethanolato‐κO)silicon, C₁₄H₁₉NO₂Si, crystallizes in two modifications. The monoclinic form, (IIm), was obtained by crystallization over a period of 2 d at room temperature; the orthorhombic form, (IIo), crystallized overnight at 248 K. The main difference between the two molecular structures involves the angles in the equatorial plane of the trigonal bipyramid around silicon. Form (IIm) has an O—Si—O angle of ca 121° and O—Si—C angles of ca 121 and 116°. In form (IIo), the corresponding angles are ∼123, 124 and 111°. There are also significant differences in the packing: (IIm) shows π stacking, whereas (IIo) does not.     

Intermolecular dihydrogen‐ and hydrogen‐bonding interactions in diammonium closo‐decahydrodecaborate sesquihydrate

The asymmetric unit of the title salt, 2NH₄⁺·B₁₀H₁₀²⁻·1.5H₂O or (NH₄)₂B₁₀H₁₀·1.5H₂O, (I), contains two B₁₀H₁₀²⁻ anions, four NH₄⁺ cations and three water molecules. (I) was converted to the anhydrous compound (NH₄)₂B₁₀H₁₀, (II), by heating to 343 K and its X‐ray powder pattern was obtained. The extended structure of (I) shows two types of hydrogen‐bonding interactions (N—H...O and O—H...O) and two types of dihydrogen‐bonding interactions (N—H...H—B and O—H...H—B). The N—H...H—B dihydrogen bonding forms a two‐dimensional sheet structure, and hydrogen bonding (N—H...O and O—H...O) and O—H...H—B dihydrogen bonding link the respective sheets to form a three‐dimensional polymeric network structure. Compound (II) has been shown to form a polymer with the accompanying loss of H₂ at a faster rate than (NH₄)₂B₁₂H₁₂ and we believe that this is due to the stronger dihydrogen‐bonding interactions shown in the hydrate (I).     

catena‐Poly­[[(pyridin‐4‐ol‐κN)silver(I)]‐μ‐pyridin‐4‐olato‐κ2N:O]

The title complex, [Ag(C₅H₄NO)(C₅H₅NO)]_n, consists of a polymeric neutral chain involving both a neutral pyridin‐4‐ol ligand and a deprotonated pyridin‐4‐olate monoanion. The Ag^I atom shows a T‐shaped coordination geometry, defined by one N atom of the pyridin‐4‐ol and one O and one N atom of two independent pyridin‐4‐olate bridges; the N—Ag—N moiety is approximately linear. The polymeric chains are connected via strong O—H⋯O hydrogen bonds and offset π–π interactions into a three‐dimensional network.     

catena‐Poly[[(1,10‐phenanthroline‐κ2N,N′)manganese(II)]‐di‐μ‐salicylato‐κ4O:O′]

In the title polymeric complex, [Mn(C₇H₅O₃)₂(C₁₂H₈N₂)]_n, the Mn^II atom is located on a twofold axis and displays a distorted octa­hedral coordination geometry, formed by four salicylate anions and one 1,10‐phenanthroline (phen) mol­ecule. The salicylate anions doubly bridge the Mn^II atoms to form one‐dimensional polymeric chains. A comparison of Mn—O bond distances with the corresponding Mn—O—C angles suggests a significant electrostatic content in the Mn—O bonds. A face‐to‐face distance of 3.352 (7) Å between neighbouring parallel phen planes indicates π–π stacking inter­actions between polymeric chains.     

A novel two‐dimensional coordination polymer: poly[diaquatetra‐μ2‐chlorido‐[μ2‐2,2′‐(piperazine‐1,4‐diium‐1,4‐diyl)diacetate]dicadmium(II)]

In the crystal structure of the title two‐dimensional metal–organic polymeric complex, [Cd₂Cl₄(C₈H₁₄N₂O₄)(H₂O)₂]_n, the asymmetric unit contains a crystallographically independent Cd^II cation, two chloride ligands, an aqua ligand and half a 2,2′‐(piperazine‐1,4‐diium‐1,4‐diyl)diacetate (H₂PDA) ligand, the piperazine ring centroid of which is located on a crystallographic inversion centre. Each Cd^II centre is six‐coordinated in an octahedral environment by an O atom from an H₂PDA ligand and an O atom from an aqua ligand in a trans disposition, and by four chloride ligands arranged in the plane perpendicular to the O—Cd—O axis. The complex forms a two‐dimensional layer polymer containing [CdCl₂]_n chains, which are interconnected into an extensive three‐dimensional hydrogen‐bonded network by C—H...O, C—H...Cl and O—H...O hydrogen bonds.     

Characterisation and coagulation performance of polysilicate-ferric-zinc

A new type of coagulant, polysilicate-ferric-zinc (PSFZn) with different Fe/Zn molar ratios, was synthesised using water glass (industrial grade, w(SiO₂) = 21 mass %, ρ = 1.34 × 10³ kg m^?3, modulus = 3.2), FeSO₄ · 7H₂O, ZnSO₄, and NaClO₃ by way of co-polymerisation in the same (Fe + Zn)/Si molar ratio based on polysilicate-ferric (PSF). The effect of the Fe/Zn molar ratios on the morphology and structure was systematically investigated using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analysis. Three samples, namely PSFZn4, PSFZn1, and PSFZn0.25, represented Fe/Zn molar ratios of 4, 1, and 0.25, respectively, and were selected for a comparative study while a constant (Fe + Zn)/Si molar ratio equal to 1 was maintained. Accordingly, PSFZn was found to be a complex compound rather than a simple mixture of raw materials. With the decrease in Fe/Zn, a great change occurred in the surface morphology, from a tetrahedral cluster structure to a lamellar structure. The Fe—O and Fe—O—Si bonds were gradually replaced by Zn—O and Zn—O—Si. However, the crystalline peaks were more obvious with the increase in the number of zinc ions; hence the new polymer would be formed from iron, zinc, and polysilicate. In addition, the coagulation performance of PSFZn was investigated using a surface water sample. PSFZn4 exhibited a better coagulation performance than the other PSFZn coagulants. Additionally, the trends in changes in pH with different coagulation times after adding PSFZn were studied relative to PSF and FS. The replacement of zinc ions with iron ions could effectively counter the rapid decrease in pH. The effect of settling time on the coagulation efficiency was also investigated. PSFZn4 exhibited a better settlement performance than PSF and poly aluminium chloride (PAC). Hence, the partial substitution of zinc salt with iron salt not only addresses the inadequacies of iron salt but also improves the coagulation efficiency of zinc salt in water treatment.     

cis‐Bis(2,2′‐bipyridyl‐N,N′)dichlorosilicon diiodide

The crystal and molecular structure of the title compound, C₂₀H₁₆Cl₂N₄Si²⁺·2I^?, has been determined at 173 K. To our knowledge, this is the first crystal structure of a silicon tetrahalide complex with a bidentate base as a ligand. The two chloro ligands are cis relative to each other. The Si—N bonds trans to a chloro ligand are longer than the Si—N bonds trans to an Si—N bond. This feature is observed for the majority of M(bipy)₂Cl₂ (M = metal and bipy = 2,2′‐bipyridyl) complexes, but it does not hold for all structures retrieved from the Cambridge Structural Database. The two pyridyl rings of each bipyridyl unit are nearly coplanar, whereas the bipyridyl units are almost perpendicular to each other. The two I^? ions are more than 5 Å from the silicon centre. As a result, the compound can definitely be described as ionic. The crystal packing is stabilized by short C—H?I contacts.     

[Perfluorosulfonate ionomer]/[SiO2-TiO2] nanocomposites via polymer-in situ sol-gel chemistry: Sequential alkoxide procedure

In situ sol-gel chemistry was used to create inorganic/perfluoro-organic hybrids wherein titanium oxide outer regions of SiO_2[1—x/4](OH)_x nanoparticles, which were preformed in Nafion® membranes, were created by postreaction with tetrabutyltitanate (TBT). U-shaped Si and Ti distributions across the membrane thickness direction were determined via x-ray energy dispersive spectroscopy. Ti/Si ratio profiles are also U-shaped, indicating more Ti relative to Si in near-surface regions. IR spectroscopy verified structural bonding of TiO₄ units onto SiO₂ nanoparticles and indicated that alkoxide hydrolysis is not complete. Reacted silicon oxide nanophases retain the topological unconnectedness possessed by the corresponding unreacted phase. IR bands signifying molecular loops and linear fragments of Si(SINGLE BOND)O(SINGLE BOND)Si groups are seen. ²⁹Si solid-state NMR spectroscopy indicated that, for an inorganic uptake of 16.3 wt %, the Q³ state of SiO₄ is most populated although Q⁴ is only slightly less prominent and Q² and Q¹ are either small or absent. The silicon oxide component, although not being predominantly linear, retains a measure of uncondensed SiOH groups. Tensile stress vs. strain analyses suggested that TBT postreaction links nanoparticles, causing them to be contiguous over considerable distances. This percolative intergrowth occurs in near-surface regions generating a glassy zone. © 1996 John Wiley & Sons, Inc.     

BaY2Si3O10: a new flux‐grown trisilicate

BaY₂Si₃O₁₀, barium diyttrium trisilicate, is a new silicate grown from a molybdate‐based flux. The structure is based on zigzag chains, parallel to [010], of edge‐sharing distorted YO₆ octa­hedra, linked by horseshoe‐shaped trisilicate groups and Ba atoms in irregular eight‐coordination. The layered character of the structure is caused by a succession of zigzag chains and trisilicate groups in planes parallel to (01). The Ba atoms occupy narrow channels extending parallel to [100]. The mean Y—O, Si—O and Ba—O bond lengths are 2.268, 1.626 and 1.633, and 2.872 Å, respectively. The two symmetry‐equivalent terminal SiO₄ tetra­hedra in the Si₃O₁₀ unit adopt an eclipsed conformation with respect to the central SiO₄ tetra­hedron; the Si—O—Si and Si—Si—Si angles are 136.35 (9) and 96.12 (4)°, respectively. One Ba, one Si and two O atoms are located on mirror planes; all remaining atoms are in general positions. The geometry of isolated trisilicate groups in inorganic compounds is briefly discussed.     

catena‐Poly[[diaquadiisothiocyanatoiron(II)]‐μ‐4,4′‐bi‐1,2,4‐triazole]: a one‐dimensional coordination polymer

In the title complex, [Fe(NCS)₂(C₄H₂N₆)₂(H₂O)₂]_n, the Fe^II atom is on an inversion centre and the 4,4′‐bi‐1,2,4‐triazole (btr) group is bisected by a twofold axis through the central N—N bond. The coordination geometry of the Fe^II atom is elongated distorted FeN₄O₂ octahedral, where the cation is coordinated by two N atoms from the triazole rings of two btr groups, two N atoms from NCS⁻ ligands and two water molecules. Btr is a bidentate ligand, coordinating one Fe^II atom through a peripheral N atom of each triazole ring, leading to a one‐dimensional polymeric (chain) structure extending along [101]. The chains are further connected through a network of O—H...N and C—H...S hydrogen bonds.